1. Field of the Invention
The present invention is directed to a drawn arc stud welder apparatus and method, and more particularly to a portable drawn arc stud welding apparatus and method providing high current output in short time intervals.
2. Description of the Related Art
Stud welding is the process of welding a metal stud, acting as an electrode, to a metal surface, without penetrating the surface. The stud welding process and welder apparatus use a gun where the stud is inserted into the gun to be fastened to a base metal. The gun is positioned over the base metal, with the stud touching. A power supply delivers a high current that starts to flow through the stud to the base metal by the user depressing the trigger of the gun. As the current starts, the stud is pulled back about xe2x85x9 inch, thereby creating an arc. After 0.2 to 1.2 seconds, the current is stopped and the stud is thrust into the created molten puddle, securing the stud to the base metal.
U.S. Pat. No. 5,662,820 generally describes a process for drawn arc stud welding using a control or regulation of the current flow of the main current electric arc.
Inverter-type power technology has been adopted for welding processes and apparatus. The first inverter welder called PowCon was introduced around 1976. The inverter power technology has replaced the conventional power supplies for welders in many applications.
However, inverter-type power technology generally has been considered not suitable for stud welding applications. This is because there are repeated high current surges, 800 to 2000 Amperes (A), delivered during short time intervals of 0.1 to 1.5 seconds during the drawn arc stud welding process. The conventional inverter power unit using single sided cooled power semiconductor silicon chips increase their temperature due to their inferior cooling so much they have not been suitable for stud welding. This has forced the stud welders to be much heavier, e.g., up to 750 lb., than welders, e.g., of 80 lbs. in weight, using inverter power units for other types of applications.
Today""s conventional technology for fastening studs is accomplished by a stud welder using a heavy 50/60 Hz transformer/rectifier. This significantly contributes to the overall heavy weight of the stud welder apparatus.
A stud welder LBH 1400 from BTH Heberle Gmbh, Germany, delivers 1400 Amps capable of welding ⅝ inch (16 mm) full base studs and weighs 300 lb. (135 Kg.). This stud welder is a conventional transformer/rectifier type, weighing as much as conventional welding machines. It consists of a transformer and SCR bridge which enables the current to vary from 0 amps to 1400 A.
A stud welder DS 312 from OBO Betterman, is capable of delivering 900A and weighs 152 lb. (69 Kg).
A stud welder Nelweld 3000 from Nelson is capable of delivering 1400 A and weighs 725 pounds.
All of the above stud welding machines are 50/60 HZ based on transformer SCR phase angle control.
Another stud welder machine from Nelson uses an inverter-type power supply capable of delivering 800 A, 6% duty cycle and weighing 36 lbs (16 Kg). This machine, however, is based on IGBT transistors in an inverter circuit. This inverter-based IGBT power semiconductor is capable of carrying only 20% of the current than an inverter-based SCR power semiconductor is capable of. The power diode is also only single-side cooled and therefore also capable of only delivery of 25% of the current than the power diode used for the invention as described hereafter.
Patent publication WO 99/31681 describes a planar-type transformer suitable for inverters. This patent publication mentions that this type of transformer is suitable for inverters for stud welding, in addition to other types of inverters.
Patent publication EP0474031A3 relates to an inverter-type of power control unit for stud welding and describes the function of an inverter.
Patent publication JP54-025247 relates to a power source for stud welding and describes a circuit to keep the current constant and thereby deliver constant heat. The stud is melted off thereby increasing the arc length. When the arc length increases the arc voltage also increases. If the arc current is kept constant, the power in the arc increases and melting off speed increases. This is a run off condition, stopped by limited supply voltage and duration of the stud process. This method does not use a power source designed to deliver constant power.
Stud welders and methods in the related art continue to have problems because they cannot deliver repeated high currents in a short duration without sacrificing other significant functions and conditions, such as reliability, weight, manufacturing costs, and the like.
One aspect of the invention is to provide a stud welder apparatus and method that overcome the problems of the conventional stud welding apparatus and methods.
Another aspect of the invention is to provide a stud welder apparatus and method capable of currents of 1000 A or greater, and which enables such high currents to be delivered under approximately a second without sacrificing function, reliability or other operational conditions.
Yet another aspect of the invention is to provide a stud welder apparatus using an inverter power supply, but which reduces the extreme stress on the power semiconductors due to the high currents and resulting high and rapid temperature swings.
Another aspect of the invention is to provide a stud welder apparatus which is not only capable of high currents in short time durations, but which is more portable by being lighter in weight.
One aspect of this invention is to provide a stud welder apparatus and method employing an inverter, which is very suitable for delivering high current during short time intervals, by using sturdy medium frequency double-sided cooled SCR""s and double-sided cooled power diodes.
Another aspect of this invention is to provide a stud welder inverter very suitable to deliver constant power to the arc, thereby guaranteeing constant energy being delivered to each stud or from stud to stud.
Another aspect of the invention is to provide a stud welder capable of measuring the resistance in the circuit without the arc, by sending a small current through the cables and stud in order to measure the resistance. This information is used to keep the true arc power constant by calculating the voltage drop in the cable and multiply by the current preset on a digital display and subtracting this from the voltage supplied in order to calculate the arc voltage. This true arc voltage is also used to automatically control the arc distance by measuring the total voltage and subtracting the preset current multiplied by the measured resistance to get the true arc voltage. This true arc voltage is continuously monitored and calculated and kept constant by moving the stud downwards as it melts off, created by the current.
Yet another aspect of the invention is to provide a stud welder with a high voltage generator that, when the base material is coated with paint, grease or corrosion, a high voltage pulse is applied between the tip of the stud and base material, penetrating the paint and providing a current path for following stud current. This function makes it possible to provide improved stud welding even on painted material.
Another aspect of the invention is to provide a stud welder inverter that makes it possible to control the shape of the pulse 50 times faster than when using 50/60 Hz. This feature makes it possible to use the first millisecond to ramp up from 0 Amp to the set amps, reducing spatter and loss of material.
Another aspect of this invention is to provide a stud welder having a drawn arc stud welding processing circuit with an electrical storage device to reduce current surge.
Various of the above aspects can be attained by a stud welder apparatus comprising a drawn arc stud applying device and a drawn arc stud processing circuit that delivers a current of 1000 amps (A) or greater to the drawn arc stud applying device, the processing circuit including an inverter having at least one double-sided cooled switching semiconductor.
For the above stud welder apparatus, as embodied herein, the inverter includes double-sided cooled secondary side diode semiconductors.
For the above stud welder apparatus, as embodied herein, the switching semiconductor can comprise double-sided cooled primary side SCR semiconductors.
For the above stud welder apparatus, as embodied herein, the processing circuit delivers the current in short intervals of approximately 0.20 to 1.2 seconds for applying studs.
For the above stud welder apparatus, as embodied herein, the processing circuit can further include a high voltage generator and wherein the processing circuit applies a voltage at approximately the same time as a spark from the gun to penetrate an insulating layer on a base to be stud welded and create a conductive path for the stud current.
Various of the above aspects also can be attained by stud welder apparatus comprising a drawn arc stud applying device and a drawn arc stud processing circuit that provides a constant power to the drawn arc stud applying device, the processing circuit including an inverter having at least one double-sided cooled switching semiconductor.
For the above stud welder apparatus, as embodied herein, the processing circuit can maintain the frequency constant to provide the constant power.
For the above stud welder apparatus, as embodied herein, the processing circuit can measure the current, multiply the current and voltage, and adjust the current to provide the constant power.
For the above stud welder apparatus, as embodied herein, the processing circuit can measure the voltage, multiply the current and voltage, and adjust the voltage to provide the constant power.
Various of the above aspects also can be attained by a stud welder apparatus comprising a drawn arc stud applying device; and a drawn arc stud processing circuit that measures the progress of making the stud and stops a supplying of current to the stud applying device if the progress indicates that the stud will not receive sufficient energy at the end of the stud process in sufficient time that the stud making process can be stopped before an unacceptable stud has been created.
Various of the above aspects also can be attained by a stud welder apparatus comprising a drawn arc stud applying device; and a drawn arc stud processing circuit that continuously measures the degree of melting off when making the stud and stops delivery of energy to the stud applying device if the melting off progress indicates that the stud will not receive sufficient energy at the end of the stud process in sufficient time that the stud process can be stopped before an unacceptable stud has been created by pulling back the stud before a molten stud has cooled down.
Various of the aspects also can be attained by a stud welder apparatus comprising a drawn arc stud applying device; and a drawn arc stud processing circuit that, after the current starts to be delivered, increases the arc length caused by current melting of the stud, and moves the stud towards a base metal to be welded with a speed equal to the stud melting speed, thereby keeping the arc length constant by measuring the arc voltage and regulating the position of the stud to achieve a constant set arc voltage.
Various of the aspects also can be attained by a stud welder apparatus comprising a drawn arc stud applying device; and a drawn arc stud processing circuit that measures the resistance of the stud, cables and gun without an arc voltage, the circuit delivering a reduced current of approximately 10 amps while the stud in the gun touches a base metal to be welded, measuring the resistance before the arc is established, calculating arc voltage, and controlling the movement back of the stud to achieve the desired arc voltage.
For the above stud welder apparatus, as embodied herein, the processing circuit can increase the current with a controlled rate.
For the above stud welder apparatus, as embodied herein, the processing circuit can decrease the current with a controlled rate.
For the above stud welder apparatus, as embodied herein, the processing circuit, starting from the start of the stud process with the arc length and not touching a base metal to be welded with a stud, can deliver a voltage spike powerful enough to make a spark between the tip of the stud and base metal to be welded.
Various of the above aspects also can be attained by a stud welder apparatus comprising a drawn arc stud applying device; and a drawn arc stud processing circuit that measures energy at regular time intervals, extrapolates a forecasted ending energy based upon a predetermined energy, and adjusts at time intervals a current to the stud applying device so that the ending energy is correct.
For the above stud welder apparatus, as embodied herein, the processing circuit can calculate by extrapolation total energy that will be delivered after the stud process is completed by calculating continuously during the stud process an accumulated watt seconds per accumulated millisecond and continuously adjusting the current so as to arrive at a total desired watt seconds when the stud process is terminated.
Various of the above aspects also can be attained by a stud welder apparatus comprising a drawn arc stud applying device; and a drawn arc stud processing circuit that stores energy during periods of no stud current and discharges the energy during a time period when current is needed to apply the stud.
These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.